This letter proposes a deadbeat current controller for isolated bidirectional dual-active-bridge dc-dc converter (IBDC). The controller uses an enhanced single phase shift (ESPS) modulation method by exploiting pulse width as an extra control variable besides phase shift ratio the only control variable of the conventional single phase shift (CSPS) modulation. The current reference can be tracked within one switching cycle during the bidirectional power transmission and transition of the two directions. Deadtime effect is studied and the compensation method for the controller is presented. Parameter robustness is analyzed by mathematical derivation and the online auto-tuning method for the inductance is presented. The proposed deadbeat current controller is simple and easy for implementation. Moreover, it shows superior dynamic performance, which is verified by experimental results during the transient processes of the converter. The effectiveness of the auto-tuning method is also validated by the prototype experiment.

Multiport power electronic transformers (PET) are widely used in modern power systems to facilitate flexible interconnection between various ac or dc buses, power sources, and loads. However, due to the wide range of “source-load-storage” operating points, achieving efficient operation of the isolated dc–dc converter in the PET can be challenging. This letter focuses on the modular multiactive bridge (MMAB) converter in the PET, and proposes an optimization modulation scheme based on reactive power minimization (RPM) to improve efficiency. The RPM scheme utilizes a simple reactive power open-loop and active power closed-loop control structure that can be modulated online without the use of look-up tables. Importantly, this generalized method not only significantly improves efficiency, but can also be extended to any number of ports. Finally, experimental results are presented to validate the theoretical analysis and effectiveness of the RPM scheme.

For the problem of narrow soft-switching range and low efficiency of dual active bridge (DAB) converter in wide voltage range, this paper proposes a single-sided asymmetric duty modulation (SSADM) strategy, which contains only two control degrees of freedom, and significantly improves the soft-switching performance and efficiency at light load. Firstly, the potential advantages of asymmetric duty modulation (ADM) method are described through waveforms. The principle of determining which full bridge to adopt the ADM is given and the working principle of SSADM is described. Secondly, a linear pulse logic combination analysis of SSADM in time domain is performed to establish a complete steady-state mathematical model. To solve the analytical expression for the optimal solution of SSADM, the peak-to-peak value of the inductor current with simple expression is chosen as the optimization objective, and the global optimal solution of SSADM is solved based on the Karush-Kuhn-Tucker (KKT) condition, and the voltage closed-loop control strategy of SSADM is presented. In addition, the soft-switching range of SSADM is analyzed. Finally, the experimental platform of DAB converter based on SiC device is built. Compared with other modulation strategies, SSADM shows better soft-switching performance with significant efficiency improvement, which is verified by the experimental results.

The electromagnetic interference issues, such as high-frequency oscillation (HFO) caused by the high dv/dt and parasitic elements, have been becoming a challenge in modern power electronics. Modular-multiactive-bridge (MMAB) converter, in which active bridge modules are linked with high-frequency transformers, is a typical power converter with a large number of switching semiconductor and magnetic devices. The mechanism of HFO in MMAB is studied by the analysis of the oscillation tank first. Then, from the perspective of the oscillation tank and the excitation source itself, two suppression strategies, including the passive voltage clamping method and active selected harmonic elimination general phase-shift modulation method, are proposed, respectively. Finally, the effectiveness of both methods is verified and compared by experimental results. The research results in this letter can be utilized in other topologies, such as dual active bridge, and may provide some inspiration to solve the similar HFO problem.

Multiactive bridge (MAB) converters are attracting increasing attention due to their advantages of mutual electrical isolation and bidirectional power flow capability among different ports. However, the presence of transient dc bias in MAB can increase the current stress and lead to transformer saturation, thus affecting the system reliability. This letter establishes a quantitative and general description of the transient dc bias based on the instantaneous middle current of the high-frequency transformer and proposes a general dynamic modulation method to eliminate the bias, which is robust irrespective of the phase-shift modulation methods and the power flow directions. Also, it works at both the normal and startup modes. More importantly, the proposed method can ensure that the high-frequency transformer current reaches to new steady state without transient dc bias within one half cycle. Finally, the MAB experimental prototypes, including a triple active bridge and a modular MAB with a high-frequency ac bus, are built to verify the superior performance of the proposed method.

The dual-active-bridge converter (DAB) has attracted tremendous attention in recent years. However, its EMI issues, especially the high-frequency oscillation (HFO) induced by the dv/dt and parasitic elements of the transformer, are significant challenges. The multi-active-bridge converter (MAB) based on the multi-winding transformer also faces similar problems, which are even more complicated. This article investigates the HFO of active-bridge-transformer-based DC/DC converters including DAB and MAB. Firstly, the general HFO model is studied using the analysis of the AC equivalent circuit considering the asymmetrical parameters. Ignoring the AC resistance in the circuit, the high-order model of the voltage oscillation could be reduced to a second-order system. Based on the simplified model, the oscillation voltage generated by an active bridge is analyzed in the time domain. Then, a universal active voltage-oscillation-suppression method-selected harmonic-elimination phase-shift (SHE PS) modulation method is proposed. The impacts of the system parameters on the method are also revealed. The experimental results show the excellent performance of the proposed active suppression method, with voltage spike amplitude (VSA) reductions of 92.1% and 77.8% for the DAB and MAB prototypes, respectively.